This invention relates to master cylinder assemblies, and more particularly to a master cylinder assembly in which the master cylinder includes a boost feature. The boost feature includes an electric motor actuated feature forming a part of the master cylinder assembly.
Master cylinders are in wide use in various industries, but particularly in the motor vehicle industry wherein they serve in conjunction with an associated slave or wheel brake cylinder located at each of the wheels of the vehicle. Each wheel brake cylinder is supplied with pressurized fluid when an operator depressing the brake pedal of the vehicle actuates the master cylinder. Although manual actuation of the master cylinder can be effective to produce the desired resultant action at the associated brake cylinder, often it is desirable to provide power-assist operation of the master cylinder.
Many current brake systems include such a power-assist feature using engine vacuum to boost the operation of the master cylinder. In a system where engine vacuum is not available, such as in an electric-powered vehicle, it would be desirable to provide a brake boost feature that provides similar functionality as that of vacuum or other boost schemes. It would be further advantageous to provide a master cylinder having a non-vacuum boost feature in combination with a manual actuation feature in order to ensure continuous operation of the brake system in the event the boost feature becomes disabled.
The object of this invention is directed to the provision of an improved master cylinder assembly. More particularly, this invention is directed to the provision of a power operated master cylinder assembly especially suitable for use in a braking system of a motor vehicle.
In one aspect of the invention, the master cylinder assembly comprises a motor having a housing; a hydraulic master cylinder including a housing rigidly connected with a transmission housing, wherein the master cylinder includes a cylinder defining an elongated bore, a piston movable linearly and slidably in the bore, inlet means in the cylinder for admitting hydraulic fluid into the bore from a reservoir and an outlet fitting in the cylinder communicating with the bore and operative to convey hydraulic fluid out of the bore for delivery to a braking device in response to linear movement of the piston in the bore. An input rod is positioned to effect movement of the piston. In addition to the input rod, a hollow ball screw assembly is separately operative in response to actuation of the input rod by a brake pedal to move the piston linearly in the bore. This arrangement provides a simple and compact drive mechanism with a manual push through especially suitable for any situation requiring a power boosted manual brake master cylinder.
Another aspect of the invention provides a master brake cylinder assembly including a hydraulic master cylinder with a piston slidably positioned in a cylinder. A hollow ball screw assembly is positioned to advance the piston in response to actuation of a motor and an input rod extends through the hollow ball screw assembly to apply an input force to the piston independently of the hollow ball screw assembly.
Other aspects of the invention provide a hydraulic master brake cylinder assembly wherein the cylinder defines an elongated bore, inlet means in the cylinder for admitting hydraulic fluid into the bore from a reservoir, and an outlet fitting in said cylinder communicating with said bore and operative to convey hydraulic fluid out of the bore for delivery to a brake device in response to linear movement of the piston in the bore.
Other aspects of the present invention provide an assembly further including sensing and control devices to sense the input force and control the motor responsive to the brake input force. The sensing device can include a differential force sensing assembly positioned adjacent an output end of the input rod. The differential force sensing assembly can include an elastomeric member positioned at the output end of the input rod. The output end of the input rod can include a position sensor associated therewith. The differential force sensing assembly can include at least one magnet associated with an output button, the output button contacting the piston. Compression of the elastomeric member causes relative movement between the position sensor and the magnet.
Other aspects of the present invention provide a transmission to drivingly connect the motor and hollow ball screw assembly. The transmission can include at least two pulleys, one of which is connected to the motor and the other of which is connected to the ball screw assembly, the at least two pulleys being drivingly connected by a belt. The transmission can further include a clutch. The clutch, when activated, couples the transmission to the motor. The clutch, when deactivated, allows the transmission to turn freely. The motor can include a primary motor and a secondary motor. The primary motor and the secondary motor each have a pulley connected thereto, the transmission further comprising an idler pulley positioned between the primary and secondary motor pulleys. The primary motor is a high current/high torque motor for fast response and high load capacity. The secondary motor is a motor requiring lower current and producing lower torque than the primary motor.
Other aspects of the invention provide a position sensor positioned adjacent the idler pulley in the transmission adapted to detect rotation of the idler pulley. The idler pulley can include a shaft extending therefrom, the shaft including at least one magnet, the magnet positioned adjacent the transmission position sensor.
Another aspect of the present invention provides a boost assembly for a hydraulic master cylinder including an electric motor. The motor rotatably drives a ball nut. A hollow screw is positioned within and threadably engaged to the ball nut, the screw having an end positioned to advance a piston of the hydraulic master cylinder when rotation of the motor linearly advances the screw. An input rod extends through the screw, the input rod including an input end positioned to receive a brake input force and an output end positioned to advance the piston responsive to the brake input force. A sensing and control means is provided to sense the brake input force and control the motor responsive to the brake input force.
Another aspect of the present invention provides a method of providing a boost force to a hydraulic master cylinder including compressing a reaction disc. A change in position of the reaction disc based on the extent of compression of the reaction disc is detected. An input force is determined based on the detected change in position and a boost force is applied based on the determined input force.
Other aspects of the present invention provide an application of the boost force that includes activating a boost motor based on the determined input force. The determination of the input force can include comparing the detected change in position to a predetermined change in position and activating the boost motor if the detected change meets or exceeds the predetermined change in position.
Another aspect of the present invention provides a system for providing a boost force to a hydraulic master cylinder including means for compressing a reaction disc, means for detecting a change in position of the reaction disc based on the extent of compression of the reaction disc, means for determining an input force based on the detected change in position and means for applying a boost force responsive to the determined input force.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.